So then if I went more off the beaten path and stuck with Drew for a girl, what names could I put with Drew as a double first name so schools, teams and government will know, "hey, this is a little girl!"?

Drew-- with the middle name Waverly, this is simply too unisex. Unfortunately there aren't any common female names that can be abbreviated or nicknamed Drew. Phoebe- this is a great choice-- it's uncommon, and even though it's much much more classic than her sister's name Scout, it has a very plucky and sunny feel that will mesh well. PhoebeWaverly has a fun flow; the vowels at the end of each word are very slightly different so it doesn't rhyme exactly.Stella- if you're happy to continue the S trend, I think this is your best pick. StellaWaverly sounds perfect (the Ls subtly reinforce each other), and even though the name is being given frequently, it still sounds fresh.Sadie- Sadie is a good style match for sister Scout, but it's a nickname (for Sarah) rather than a full given name, and I'd prefer Stella or Phoebe since I think they'll work better for a grown woman.Wynn- this is actually the masculine spelling; the feminine spelling has an e (Wynne). I actually quite like WynneWaverly-- it's very unexpected, and I like the alliteration. This is actually my favorite suggestion.

Boy listSullivan (Sully) - adorable nickname; a bit longer than his siblings' names but it's an Irish surname like Shea, and balances well with Scarlett.Nate- not complete enough as a given name. Much prefer Nathan or Nathaniel. (You could also get there from Jonathan, Donato, Ignatius or Renato, but I'm not sure these names are your style). NathanielJames is a very handsome name.Drew- works well on a boy. DrewJameson sounds great, though I slightly prefer the more formal AndrewJames as I think it will work better for him throughout his life.Cash- don't care for Cash. I wouldn't want to name a child "money." Now, Nash would really hit the right notes for your family-- what do you think of NashJameson?